1. Field of the Invention
The present invention relates to a semiconductor device and a method of fabricating the same, and in particular, to a semiconductor device comprising a ferroelectric memory employing a highly ferroelectric film as a capacitive insulator and a method of fabricating the same.
2. Description of the Related Art
In recent years, attention has been focused on a semiconductor memory called a FeRAM (Ferroelectric Random Access Memory) comprising a capacitor that employs a ferroelectric film for a capacitive insulator, as the coming generation of a nonvolatile memory.
With a conventional ferroelectric memory, a ferroelectric capacitor comprising a capacitive insulator made up of a ferroelectric film, and an upper electrode and a lower electrode with the capacitive insulator interposed between the electrodes is formed on a semiconductor substrate with an integrated circuit comprising transistors and so froth, formed thereon.
Further, a silicon oxide film serving as an interlayer insulator is formed on top of the semiconductor substrate and the ferroelectric capacitor, and after removal of water constituents contained in the interlayer insulator by heat treatment, contact holes reaching the integrated circuit or the ferroelectric capacitor, provided on the semiconductor substrate, are formed in the interlayer insulator.
A metal pattern made of material such as aluminum (Al), titanium (Ti), or tungsten (W), and so forth is formed inside these contact holes, and is electrically connected to the integrated circuit and the ferroelectric capacitor, respectively. Further, a passivation film serving as a protection film is formed on the respective metal patterns.
With a capacitor making up a conventional FeRAM, an insulating film made of a metal oxide such as strontium bismuth tantalate (SrBi2Ta2O9) called as SBT, lead zirconate titanate (Pb(Zr, Ti)O3) called as PZT, and so forth is used for a capacitive insulator made up of a ferroelectric film.
Further, a noble metal is generally used as the constituent material of the upper electrode and lower electrode. This is because at the time of forming a highly ferroelectric film, and at the time of improving the film quality of the capacitive insulator after the formation of the capacitor, the electrodes making up the capacitor come to be exposed to a high temperature oxidizing atmosphere, so that oxidation resistance is highly required of the constituent material of the electrodes. Particularly, in the case of the conventional ferroelectric capacitor, platinum (Pt) is used as a constituent material of the electrodes from the viewpoint of cost, process stability, ease in the fabrication of the ferroelectric film, and excellent workability.
In developing the present invention relating to a semiconductor device comprising a ferroelectric capacitor, particularly using a noble metal having a catalytic action as a constituent material of electrodes, attention has been focused on hydrogen molecules evolved due to oxidation of the surface of metal patterns made of Al, Ti, W, or so forth in the course of water constituents such as constitution water, contained in a silicon oxide film making up interlayer insulators, adsorption water evolved in a cleaning process, and so forth undergoing thermal diffusion following heat treatment applied in later stages.
It is therefore an object of the invention to provide a method of fabricating a semiconductor device comprising a ferroelectric memory maintaining satisfactory memory characteristics by decreasing evolution of the hydrogen molecules, and suppressing evolution of hydrogen atoms that cause metal oxides of a ferroelectric film, produced by the agency of the catalytic action of the constituent material of the electrodes, to undergo reduction. Further, it is another object of the invention to provide a method of fabricating a semiconductor device capable of protecting a ferroelectric capacitor from water constituents evolved in fabrication steps after the formation of the ferroelectric capacitor.
In accordance with a first aspect of the invention, there is provided a method of fabricating a semiconductor device comprising:
a step of forming a capacitor comprising a lower electrode formed on a semiconductor substrate, a capacitive insulator made up of a metal oxide film, formed on the lower electrode, and an upper electrode formed on the capacitive insulator;
a step of forming a metal pattern to be electrically connected to the electrodes of the capacitor;
a step of forming a first protection film for coating at least a side face of the metal pattern; and
a step of forming a water constituents diffusion preventive film on the side face and top face of the metal pattern through the intermediary of the first protection film.
Further, in accordance with a second aspect of the invention, there is provided a method of fabricating a semiconductor device comprising:
a step of forming a capacitor comprising a lower electrode formed on a semiconductor substrate, a capacitive insulator made up of a metal oxide film, formed on the lower electrode, and an upper electrode formed on the capacitive insulator;
a step of forming an interlayer insulator on top of the capacitor and the semiconductor substrate;
a step of forming a hole in the interlayer insulator for exposing the top face of the electrodes of the capacitor;
a step of forming a metal pattern inside the hole for electrical connection with the electrodes of the capacitor;
a step of forming an insulating film having a low water constituent content on top of the metal pattern inside the hole; and
a step of forming a water constituents diffusion preventive film on top of the metal pattern or the insulating film having the low water constituent content.
Thus, the invention can provide the method of fabricating the semiconductor device comprising the ferroelectric capacitor using a noble metal having a catalytic action as the constituent material of the electrodes, wherein evolution of hydrogen atoms, caused by the catalytic action of the constituent material of the electrodes, can be suppressed, so that the ferroelectric memory of the semiconductor device is capable of maintaining satisfactory memory characteristics.